CN104143837B - There is the inverter alternating voltage sensorless control method of parameter adaptive characteristic - Google Patents

Abstract

A kind of inverter alternating voltage sensorless control method with parameter adaptive characteristic. First with Second Order Generalized Integrator, the indifference following feature of characteristic frequency AC signal is built orthogonal filter, then use this orthogonal filter and introduce parameter adaptive control strategy, build the voltage observer of the three-phase grid-connected inverter with parameter adaptive characteristic, under biphase rest frame, to measure the grid side current signal obtained with circuit control device output bridge terminal voltage reference signal as the input of voltage observer, observe line voltage; And control in conjunction with three-phase grid-connected inverter PR under biphase rest frame, it is achieved the inverter operation when alternating voltage sensorless controls. The method can when keeping inverter control stability, avoid the problems such as integration saturated, initial value is sensitive, static error that conventional alternating voltage sensorless is likely to occur in controlling, and when grid-connected inverters impedance parameter changes, there is good adaptability.

Description

Inverter AC-voltage-sensor-free control method with parameter adaptive characteristic

Technical Field

The invention relates to a control method of a three-phase grid-connected inverter.

Background

Renewable energy grid-connected power generation systems develop rapidly in recent years, and when the renewable energy grid-connected power generation systems are connected to a power distribution network with a weak grid structure or a tail end of the power grid, the problems that the short-circuit capacity of a grid-connected point is small, the stability of the power grid is poor, and the power grid has serious voltage fluctuation, flicker, symmetrical or asymmetrical voltage drop faults and the like may exist. The intermittency and randomness of the renewable energy source itself may further deteriorate the voltage stability of the connected power system and adversely affect the stable operation of itself. In order to realize grid-connected power and current control of a renewable energy power generation system, a phase-locked loop is generally adopted in the existing grid-connected converter or inverter to obtain power grid voltage information, but the control of the phase-locked loop is easily influenced by the voltage fluctuation of a power grid, and the electric energy quality of the renewable energy grid-connected power generation system is easily reduced. Therefore, in recent years, some researchers at home and abroad begin to research the ac-free voltage sensor control which does not depend on the grid voltage signal so as to improve the robustness of the inverter grid-connected control.

Similar to the voltage sensor control, in the no-voltage sensor control algorithm, the reconstructed voltage/virtual flux linkage signal may be explicit and vector controlled; or implicit and direct power control. The existing grid voltage/virtual flux linkage reconstruction method can be roughly divided into two categories, one is a grid voltage/virtual flux linkage reconstruction method based on complex power estimation, which belongs to an open loop estimation method, has low accuracy, and is easy to cause interference due to the fact that a current differential term is contained; and the second is a power grid voltage/virtual flux linkage reconstruction method based on grid side current deviation adjustment, which belongs to a closed-loop estimation method and has higher accuracy.

Noguchi et al, in the literature "DirectPower control of PWMcConverester with non-voltage-sensor", propose a direct power control method based on a voltage-free sensor, which first uses filter inductive current and its differential term to estimate the active and reactive power on the AC side, and then performs grid voltage reconstruction. In order to reduce errors caused by differential terms, the method needs larger inductance value and sampling frequency; in addition, when the current is small, the voltage estimation accuracy may be greatly affected. Malinowski et al put forward a modified integral operation in a document 'sensorless controlled linear transformation for a new-phasePWMrecitifiers' to observe a 'virtual flux linkage' of a power grid; however, the pure integrator method has problems of integral saturation, zero drift and the like, and is sensitive to an initial value.

Patent CN201010109338.2 proposes a direct power control method for a grid-connected inverter without an ac voltage sensor, which solves the problem that the grid-connected inverter cannot work normally in the existing method due to improper selection of an initial value of an integrator in a virtual flux linkage observer of a grid-side voltage vector. Patent CN201010207412.4 proposes a control method for a high-voltage dc transmission converter without an ac voltage sensor, which realizes control without an ac voltage sensor by calculating a virtual flux linkage vector of a system.

The ac voltage sensorless control methods described in the above documents and patents generally use a flux observer based solution: and integrating the current under a synchronous coordinate system to obtain a virtual flux linkage, and indirectly calculating the voltage angle of the power grid. In order to reduce interference and improve observation accuracy, a low-pass filter is generally required to be used, but the low-pass filter has the problems of zero drift, integral saturation, steady-state error, initial value sensitivity and the like; in addition, when the voltage of the power grid is asymmetric, delay time is increased by a cascade algorithm of flux linkage observation and positive and negative sequence separation, and the dynamic response speed of the system is reduced.

Since a second-order generalized integrator (SOGI) can perform an integration operation on an alternating current with a specific frequency, the second-order generalized integrator is often used to construct a phase-locked loop in a stationary coordinate system and used for grid-connected synchronous control of a single-phase or three-phase voltage source inverter. In fact, the second-order generalized integrator can be used for constructing a Quadrature Filter (QF), outputting a pair of sinusoidal quadrature signals, and reconstructing the grid voltage, so as to implement ac-free voltage sensor control. In addition, positive and negative sequence separation can be synchronously realized by utilizing the orthogonal signals, so that the dynamic performance of the inverter under the condition of an asymmetric power grid is improved.

Disclosure of Invention

The invention aims to solve the problems of zero drift, integral saturation, steady-state error, initial value sensitivity and the like possibly existing in the control of the existing inverter no-alternating voltage sensor, enable the control of the inverter no-alternating voltage sensor to be adaptive to the change of grid-connected impedance parameters, and provide a control method of the three-phase grid-connected inverter no-alternating voltage sensor with parameter adaptive characteristics. The method can avoid the problems of integral saturation and the like which can occur in the conventional control without an alternating voltage sensor under the condition of keeping the control stability of the inverter, has the advantages of rapidness, no static error, insensitivity to an initial value and the like, and has good adaptability to the parameter change of grid-connected impedance.

The invention relates to a control method of an inverter non-alternating voltage sensor with parameter adaptive characteristics, which is characterized in that an orthogonal filter is constructed based on a second-order generalized integrator (SOGI), then a power grid voltage observer with parameter adaptive characteristics is constructed based on the orthogonal filter and by introducing a parameter adaptive control strategy, and the voltage observer is applied to a controller of a three-phase grid-connected inverter to realize the control of the inverter without the alternating voltage sensor. The method specifically comprises the following steps:

1. an orthogonal filter (QF) based on a second-order generalized integrator (SOGI) is constructed, the second-order generalized integrator comprises a second-order resonance link of sinusoidal signals, the integral operation can be carried out on sinusoidal and orthogonal flow, and the non-static tracking control can be realized on the alternating current signals with specific frequencies. The quadrature filter comprises input and output signals, a filter gain coefficient, a second-order generalized integrator, an output feedback and the like, wherein v is a filter input signal,andis the output signal of the filter and is,andis a pair of orthogonal signals, of whichIn phase with v, the voltage of the first voltage,lags v by 90 deg., k being the filter gain factor. After the AC input signal v enters the filter, it is connected with the feedback output signalThe deviation (c) passes through a filter gain coefficient k and then enters a second-order generalized integrator, and the output of the second-order generalized integratorAnd

2. and (3) constructing a voltage observer with parameter self-adaptive characteristics based on the orthogonal filter in the step (1) and introducing a parameter self-adaptive control strategy, and observing the voltage of the alternating current power grid. The input of the voltage observer with the parameter adaptive characteristic is i_αβAnd v_αβWherein i_αβFor measuring the component of the AC side current of the inverter in a two-phase stationary reference frame, v_αβControlling the components of the voltage at the bridge end output by the inverter controller in a two-phase static coordinate system; output ofThe component of the grid voltage in the two-phase stationary coordinate system is obtained for observation. Component i of the inverter AC side current in the two-phase stationary coordinate system_αβAnd the component v of the bridge end control voltage of the inverter controller in a two-phase static coordinate system_αβRespectively entering the orthogonal filters in step 1 to obtain outputAndandmathematical model based on three-phase grid-connected inverter $\left[\begin{array}{c}{u}_{\mathrm{\α}}\\ u_{\mathrm{\β}}\end{array}\right]=L\frac{d}{\mathrm{dt}}\left[\begin{array}{c}{i}_{\mathrm{\α}}\\ i_{\mathrm{\β}}\end{array}\right]+R\left[\begin{array}{c}{i}_{\mathrm{\α}}\\ i_{\mathrm{\β}}\end{array}\right]+\left[\begin{array}{c}{v}_{\mathrm{\α}}\\ v_{\mathrm{\β}}\end{array}\right]$ Deriving the components of the grid voltage in a two-phase static coordinate system

And (3) introducing an impedance parameter adaptive control strategy based on the orthogonal filter in the step 1. The grid-connected impedance parameter self-adaptive control strategyWhen the DC load of the inverter is constant, the unit power factor of the inverter is operated, the inductance parameter in the voltage observer is changed in small step length, and when the amplitude of the AC side current of the inverter is minimum, the inductance parameter is considered to be consistent with an actual value. Designing a parameter searching program min { | i | } according to the strategy, and enabling the voltage observer to input i { | i | }_αβAnd entering a min { | i | } search program to obtain an impedance value when the current amplitude is minimum, wherein the impedance value is the actual grid-connected impedance value of the inverter. Based on the method, the voltage observer has parameter adaptive characteristics.

3. The PR controller based on the step 1 and the step 2 and provided with the parameter self-adaptive characteristic is applied to a PR controller of a three-phase grid-connected inverter under an αβ coordinate system, the PR controller comprises a power outer ring based on PI, a current inner ring based on PR, a PWM modulation link and the like, wherein the power outer ring comprises a direct current side voltage outer ring and a reactive power outer ring which are used for respectively controlling direct current side voltage and reactive power, the direct current side voltage outer ring outputs active reference current controlled by the inverter, the reactive power outer ring outputs reactive reference current controlled by the inverter, the current inner ring is the PR controller under a αβ two-phase static coordinate system, and component of grid voltage output by a voltage observer under the two-phase static coordinate system① is used for calculating and obtaining the actual reactive power value of the three-phase grid-connected inverter as the feedback value of the reactive power outer loop, ② is used for coordinate transformation from a dq coordinate system to a αβ coordinate system and transforming the current reference value under the dq coordinate system output by the power outer loop PI controller into the current reference value under a αβ coordinate system, thereby realizing the three-phase grid-connected inverter control without an alternating voltage sensor based on the method of the invention.

Drawings

FIG. 1 is a simplified equivalent circuit model of a grid-connected inverter;

fig. 2 is a steady state operation phasor diagram of the grid-connected inverter, wherein fig. 2a is a steady state phasor diagram when an inductance parameter is larger than an actual value, and fig. 2b is a steady state phasor diagram when an inductance parameter is smaller than an actual value;

FIG. 3 is a block diagram of a Quadrature Filter (QF) architecture;

FIG. 4 is a block diagram of a voltage observer with parameter adaptive behavior;

FIG. 5 is a control block diagram of a three-phase grid-connected inverter without an alternating-current voltage sensor and with parameter adaptive characteristics;

fig. 6 is a simulation result of an influence on an inverter operation condition when a grid-connected impedance parameter changes in the grid voltage observer, where fig. 6a is inductance parameter change, fig. 6b is voltage amplitude change, fig. 6c is current amplitude change, and fig. 6d is inverter output reactive power.

Detailed Description

The invention is further described below with reference to the accompanying drawings and the detailed description.

Compared with a conventional three-phase grid-connected inverter control method, the AC-free voltage sensor control method provided by the invention does not use an AC voltage sensor, but uses a voltage observer constructed based on an orthogonal filter to acquire the voltage information of a power grid, and meanwhile, the voltage observer has parameter adaptability, so that the operation control of the three-phase grid-connected inverter under the condition of no AC voltage sensor is realized, and the AC-free voltage sensor control method has good adaptability when the grid-connected impedance parameter of the inverter changes.

The method comprises the steps of constructing an orthogonal filter based on a second-order generalized integrator (SOGI), then constructing a power grid voltage observer with parameter adaptive characteristics based on the orthogonal filter and introducing a parameter adaptive control strategy, and applying the voltage observer to a controller of a three-phase grid-connected inverter to realize the control of the inverter without an alternating voltage sensor.

The voltage observer can be derived according to a model of the three-phase grid-connected inverter, and is represented by the following formula:

$\left[\begin{array}{c}{u}_{\mathrm{\α}}\\ u_{\mathrm{\β}}\end{array}\right]=L\frac{d}{\mathrm{dt}}\left[\begin{array}{c}{i}_{\mathrm{\α}}\\ i_{\mathrm{\β}}\end{array}\right]+R\left[\begin{array}{c}{i}_{\mathrm{\α}}\\ i_{\mathrm{\β}}\end{array}\right]+\left[\begin{array}{c}{v}_{\mathrm{\α}}\\ v_{\mathrm{\β}}\end{array}\right]---\left(1\right)$

wherein u is_αAnd u_β、i_αAnd i_β、v_αAnd v_βThe components of the power grid voltage, the current at the alternating current side of the inverter and the output voltage of a bridge arm of the inverter in a two-phase static coordinate system are respectively shown, and L and R are respectively equivalent inductance and resistance at the output side of the inverter.

The differential term of the current exists in the formula (1), and interference is easily introduced in general calculation. The reason is that the general AC-free voltage sensor control is changed to adopt integral operation to calculate the virtual flux linkage of the power grid and indirectly obtain the voltage information of the power grid; however, the conventional virtual flux linkage method has the problems of zero drift, integral saturation, steady-state error, initial value sensitivity and the like, and the dynamic response is slow. The invention constructs the orthogonal filter based on the second-order generalized integrator, constructs the grid voltage observer by using the orthogonal filter and introducing a parameter adaptive control strategy, can better solve the current differential operation problem, effectively reduces harmonic interference, has better dynamic response speed for the three-phase grid-connected inverter control without the alternating voltage sensor based on the voltage observer, and has certain adaptability to the grid-connected impedance parameter change.

Observing the formula (1) can find that the grid voltage needs to be accurately observed, and not only needs to have an alternating current measured value with higher precision, but also needs to have accurate parameters of an inverter reactor. In actual operation, the inductance of the reactor is difficult to measure accurately and can change along with the change of environmental factors such as temperature. In addition, when the inverter is in grid-connected operation, the equivalent impedance of the line also changes along with the changes of factors such as power flow and network structure, so that the voltage of a grid-connected point is influenced, and the observation of the voltage of a power grid is adversely influenced. Therefore, the invention improves the power grid adaptability of the control without the alternating voltage sensor when the circuit parameters are changed by improving the parameter adaptive characteristic of the voltage observer.

The following describes in detail the implementation steps of the control method of the present invention:

step (1): firstly, analyzing the influence of the inverter grid-connected impedance parameter change

To illustrate the effect of circuit parameters, a simplified equivalent circuit model as shown in fig. 1 can be used, and the following assumptions can be made in the simplified model:

(1) the inverter is connected to a strong power grid, and the voltage u of the power grid is unchanged, namely, the line impedance and the reactor impedance are combined;

(2) neglecting the switching loss and the resistance of the AC side filter;

(3) the DC side of the inverter is connected with a constant resistive load and controls the voltage U of the DC side_dcAnd keeping the output power P constant, namely the output power P on the direct current side. Then the active component i of the AC side current i can be known according to the AC/DC power relation_dConstant:

whereinAngle of power factor for point of grid connection, I_loadConst is a dc-side current and is expressed as a constant.

(4) And controlling the inverter to operate at the unit power factor. When the inverter stably operates, the inverter controller outputs the grid voltage output by the observerIs directed toShafts, i.e.Due to current regulationAction of economizer, grid currentEqual to the reference value, then derived:

$\begin{array}{c}\left[\begin{array}{c}{\hat{i}}_d\\ {\hat{i}}_q\end{array}\right]=\left[\begin{array}{c}{i}_d^{*}\\ i_q^{*}\end{array}\right]=\frac{1}{{\hat{u}}_d^2+{\hat{u}}_q^2}\left[\begin{array}{cc}{\hat{u}}_d& {\hat{u}}_q\\ {\hat{u}}_q& -{\hat{u}}_d\end{array}\right]\left[\begin{array}{c}{P}^{*}\\ Q^{*}\end{array}\right]\\ =\frac{1}{{\hat{u}}_d^2}\left[\begin{array}{cc}{\hat{u}}_d& 0\\ 0& -{\hat{u}}_d\end{array}\right]\left[\begin{array}{c}{P}^{*}\\ 0\end{array}\right]=\left[\begin{array}{c}{P}^{*}/{\hat{u}}_{\mathrm{gd}}\\ 0\end{array}\right]\end{array}---\left(3\right)$

wherein,is a controller atGrid voltage and current under a coordinate system.

Since the current can be measured by a transformer, thereforeCoinciding with the actual current i. According to the formula (3),the angle between i and i should be zero. And obtaining a phasor relation diagram when the inductance parameter deviates from the actual value according to fig. 1, as shown in fig. 2, wherein fig. 2a is a steady-state phasor diagram when the inductance parameter is larger than the actual value, and fig. 2b is a steady-state phasor diagram when the inductance parameter is smaller than the actual value. Wherein the network voltage u, the active component i of the alternating current_dIs a constant value.The inductance parameter used by the inverter controller and L is the actual inductance value. It can be seen from fig. 2 that the grid voltage output by the observer does not coincide with the actual voltage due to the use of incorrect inductance parameters, and thus the actual power factor angleIs not zero. Since the actual reactive power of the grid-connected point is not zero, and the active power depends only on the DC side, therefore, the grid-connected point can not only be used for generating the active power of the grid-connected point, but also can be used for generating the active power of the grid-connected pointIf larger or smaller than L, the actual current will increase.

Therefore, when the grid-connected impedance parameter value used by the inverter controller is inconsistent with the actual value, the grid-connected impedance parameter can be corrected by judging the current amplitude value of the alternating current side of the inverter.

Step (2): a Quadrature Filter (QF) is constructed based on a Second Order Generalized Integrator (SOGI).

The second-order generalized integrator can realize the tracking of the alternating current quantity of a specific frequency, and is used for outputting a pair of orthogonal alternating current quantities to realize positive and negative sequence separation at the earliest. According to the characteristics of the output signal, the filter constructed based on the second-order generalized integrator is called a Quadrature Filter (QF), and the structure of the filter is shown in fig. 3.

As shown in fig. 3, v is the filter input signal,andfor the output signal, superscript ^ denotes the observed quantity, omega_vIs the angular frequency of the AC voltage signal, k beingA filter gain factor.

And (3): and (3) constructing a voltage observer with parameter adaptive characteristics based on the orthogonal filter in the step (2) and introducing a parameter adaptive control strategy.

Since the quadrature signal of the sinusoidal signal corresponds to its differentiated in-phase or anti-phase signal, the following can be derived based on equation (1):

$\begin{array}{c}\left[\begin{array}{c}{\hat{u}}_{\mathrm{\α}}\\ {\hat{u}}_{\mathrm{\β}}\end{array}\right]=L\frac{d}{\mathrm{dt}}\left[\begin{array}{c}{\hat{i}}_{\mathrm{\α}}\\ {\hat{i}}_{\mathrm{\β}}\end{array}\right]+R\left[\begin{array}{c}{\hat{i}}_{\mathrm{\α}}\\ {\hat{i}}_{\mathrm{\β}}\end{array}\right]+\left[\begin{array}{c}{\hat{v}}_{\mathrm{\α}}\\ {\hat{v}}_{\mathrm{\β}}\end{array}\right]\\ =-L\left[\begin{array}{c}{\hat{i}}_{\mathrm{\α}}^{\⊥}\\ {\hat{i}}_{\mathrm{\β}}^{\⊥}\end{array}\right]+R\left[\begin{array}{c}{\hat{i}}_{\mathrm{\α}}\\ {\hat{i}}_{\mathrm{\β}}\end{array}\right]+\left[\begin{array}{c}{\hat{v}}_{\mathrm{\α}}\\ {\hat{v}}_{\mathrm{\β}}\end{array}\right]\\ =-G_{\mathrm{QF}2}L\left[\begin{array}{c}{i}_{\mathrm{\α}}\\ i_{\mathrm{\β}}\end{array}\right]+G_{\mathrm{QF}1}(R\left[\begin{array}{c}{i}_{\mathrm{\α}}\\ i_{\mathrm{\β}}\end{array}\right]+\left[\begin{array}{c}{v}_{\mathrm{\α}}\\ v_{\mathrm{\β}}\end{array}\right])\\ =G_{\mathrm{VO}}{\left[\begin{array}{cccc}{i}_{\mathrm{\α}}& i_{\mathrm{\β}}& i_{\mathrm{\α}}& i_{\mathrm{\β}}\end{array}\right]}^T\end{array}---\left(4\right)$

wherein i_α、i_βFor measuring the component of the AC side current of the inverter in a two-phase stationary reference frame, v_α、v_βControlling the components of the voltage at the bridge end output by the inverter controller in a two-phase static coordinate system; output ofThe component of the grid voltage in the two-phase stationary coordinate system is obtained for observation.Andandis i_α、i_βThe output quantity after the orthogonal filter in the step (2) is marked with a symbol ^ which represents the observed quantity, whereinAndandsignals that are orthogonal to each other;andandis v is_α、v_βThe output quantities after passing through the quadrature filters of step (2), respectively, whereinAndandsignals that are orthogonal to each other; g_VOIs the transfer function of the grid voltage observer.

And (3) simultaneously introducing an impedance parameter self-adaptive control strategy by combining the orthogonal filter in the step (2). The parameter self-adaptive control strategy is characterized in that when the direct current load of the inverter is constant, the unit power factor of the inverter is enabled to operate, the inductance parameter in the voltage observer is changed in small step length, and when the amplitude of the current on the alternating current side of the inverter is minimum, the inductance parameter is considered to be consistent with an actual value. Designing a parameter searching program min { | i | } according to the strategy, and enabling the voltage observer to input i { | i | }_αβAnd entering a min { | i | } search program to obtain an impedance value when the current amplitude is minimum, wherein the impedance value is the actual grid-connected impedance value. Based on the method, the voltage observer has parameter self-adaptive characteristics for the change of the grid-connected impedance.

Based on the formula (4) and by introducing the control block diagram of the voltage observer of the impedance parameter adaptive control strategy, as shown in fig. 4, the voltage of the alternating current power grid can be observed, and meanwhile, certain adaptability is provided for the change of the grid-connected impedance parameter of the inverter.

And (4): and (4) applying the voltage observer with the parameter adaptive characteristic in the step (3) to a PR controller of the three-phase grid-connected inverter under a two-phase static coordinate system, and realizing the control of the inverter without an alternating voltage sensor.

Substituting the voltage observer into a control block diagram of the three-phase grid-connected inverter under an αβ coordinate system to realize three-phase grid connectionAc voltage sensorless control of the inverter is shown in fig. 5. The voltage observer PAVO is the voltage observer with parameter adaptive characteristics proposed in step (3), and observes the grid voltage information by using the measured grid-side current signal and the bridge-end reference voltage signal output by the inverter controller in the two-phase static coordinate system. As shown in fig. 5, K_CFor the current controller, the present invention uses a conventional PR controller.

In order to verify the effectiveness of the control method, an inverter time domain simulation model is established in MATLAB, the adopted control block diagram is shown in FIG. 5, and the simulation result is shown in FIG. 6. And keeping the direct-current voltage stable, wherein the active power load of the inverter is about 0.5p.u., and the reactive power reference value is set to be 0. Let the inductance parameter in the voltage observer change in a triangle, as shown in fig. 6a, the output current and reactive power of the inverter will also change periodically, as shown in fig. 6 b-6 d, where fig. 6b is the comparison of the actual grid voltage amplitude (U) and the voltage observer output voltage amplitude (u.ob); FIG. 6c is the inverter output current magnitude; fig. 6d shows the inverter outputting reactive power. By comparison, the minimum value of the output current of the inverter appears at the moment when the inductance is close to the rated value, the reactive power change period is the same as the inductance change period, and the amplitude change period of the current and the observed voltage is twice as long as the inductance change period. The simulation result is consistent with the theoretical analysis.

Claims (3)

1. The control method is characterized in that an orthogonal filter is constructed based on a second-order generalized integrator (SOGI), then a power grid voltage observer with parameter adaptive characteristics is constructed based on the orthogonal filter and by introducing a parameter adaptive control strategy, and the voltage observer is applied to a PR (pulse width modulation) controller of a three-phase grid-connected inverter under a two-phase static coordinate system to realize the control of the inverter without the AC voltage sensor; the quadrature filter comprises input and output signals, and a filter gain coefficient kA second-order generalized integrator and an output feedback; after the AC input signal v enters the quadrature filter, it is combined with the feedback output signalThe deviation (c) passes through a filter gain coefficient k and then enters a second-order generalized integrator, and the output of the second-order generalized integratorAndthe input of the voltage observer with the parameter adaptive characteristic is i_αβAnd v_αβWherein i_αβFor measuring the component of the AC side current of the inverter in a two-phase stationary reference frame, v_αβControlling the components of the voltage at the bridge end output by the inverter controller in a two-phase static coordinate system;the component of the grid voltage output by the voltage observer in the two-phase static coordinate system;

the component i of the measured AC side current of the inverter in a two-phase static coordinate system_αβAnd the component v of the bridge-end control voltage output by the inverter controller in the two-phase static coordinate system_αβRespectively passed through said quadrature filters to obtain outputsAnd andthen based on the following mathematical model of the three-phase grid-connected inverter:

$\left[\begin{array}{c}{u}_{\mathrm{\α}}\\ u_{\mathrm{\β}}\end{array}\right]=L\frac{d}{dt}\left[\begin{array}{c}{i}_{\mathrm{\α}}\\ i_{\mathrm{\β}}\end{array}\right]+R\left[\begin{array}{c}{i}_{\mathrm{\α}}\\ i_{\mathrm{\β}}\end{array}\right]+\left[\begin{array}{c}{v}_{\mathrm{\α}}\\ v_{\mathrm{\β}}\end{array}\right]$

deriving the network voltage to be twoComponent of the stationary coordinate system

In the above formula, u_αAnd u_βComponent of the grid voltage in a two-phase stationary frame, i_αAnd i_βIs the component of the AC side current of the inverter in a two-phase stationary frame, v_αAnd v_βThe method comprises the following steps that components of output voltage of a bridge arm of an inverter in a two-phase static coordinate system are provided, and L and R are equivalent inductance and resistance of the output side of the inverter respectively;

the parameter self-adaptive control strategy is characterized in that when the direct current load is constant, the unit power factor of the inverter is enabled to operate, the inductance parameter in the voltage observer is changed in small step length, and when the amplitude of the current on the alternating current side of the inverter is minimum, the inductance parameter is considered to be consistent with an actual value; and designing a parameter searching program according to the strategy, so that the voltage observer has parameter self-adaptive characteristics for the change of grid-connected impedance.

2. The inverter control method without the alternating voltage sensor according to claim 1, wherein the second-order generalized integrator comprises a second-order resonance link of a sinusoidal signal, can perform integral operation on sinusoidal alternating current, and can realize non-static tracking control on an alternating signal with a specific frequency.

3. The method for controlling the AC-free voltage sensor of the inverter according to claim 1, wherein the voltage observer with the parameter adaptive characteristic is applied to a PR controller of the three-phase grid-connected inverter under αβ coordinate system, the controller comprises a PI-based power outer loop and a PR-based current inner loop, and the voltage observer outputsThe method is used for the following aspects of inverter control, and realizes AC-free voltage sensor control on the three-phase grid-connected inverter:

the method comprises the following steps of firstly, calculating to obtain an actual reactive power value of the three-phase grid-connected inverter as a feedback value of a reactive power outer loop;

and secondly, the power outer loop PI controller is used for converting the coordinate from the dq coordinate system to the alpha beta coordinate system, and converting the current reference value under the dq coordinate system output by the power outer loop PI controller into the current reference value under the alpha beta coordinate system.